The present invention relates to a vessel for processing steel under vacuum, and includes a vessel body, a cover placed thereupon in a vacuum-tight manner, and a connection for a vacuum pump, whereby to heat the vessel a heating means is provided that comprises a graphite rod that extends diametrically through the vessel, with contact studs being provided at the ends of the graphite rod for the transfer of electrical power.
With graphite rod heating means for steel-processing vessels, the mounting of the graphite rod, with its connections, especially contact studs, at its ends, in the vessel body presents a problem since as the vessel body, with its inner refractory lining, is heated up, the vessel body has a different expansion characteristic than does the graphite rod. This problem is accentuated by the fact that the openings in the walls of a vessel for the graphite rod must have a vacuum-tight configuration. In this connection, the vacuum that prevails in the interior of the vessel also acts upon the contact studs of the graphite rod, and upon the other connections, and leads to an oppositely directed stress that is directed into the interior of the vessel, as a consequence of which corresponding stresses occur in the graphite rod. The result is that the heretofore known graphite rod heating means have only a relatively short service life because due to the aforementioned conditions stresses occur in the graphite rod that lead to a premature failure of the rod or at least to a nonuniform consumption of the graphite rod.
DE-OS 36 37 065 discloses a steel-processing vessel of the aforementioned general type where the graphite rod is held in an intermediate ring that is supposed to be disposed between the vessel body and the cover. With this known arrangement, the intermediate ring should be embodied in such a way that it takes into account the expansion of the graphite rod during the heating phase and at the same time follows the stress that results from the vacuum. However, it has been shown that the approach described in DE-OS 36 37 061 is technically very complicated and can be realized in only a complicated and expensive manner It is therefore an object of the present invention to provide a vacuum-tight vessel for processing steel that is provided with a graphite rod heating means where the different expansion characteristics as well as the prevailing vacuum are taken into consideration and therefore the service life of the graphite rods for the heating means is prolonged.